Polyimides and poly(amide - acids)prepared from diamines and thianthrenetetracarboxylic acid 5,5,10,10-tetraoxides



United States Patent Ofiice 3,502,625 Patented Mar. 24, 1970 Int. Cl. C08g 20/32 US. Cl. 26078 10 Claims ABSTRACT OF THE DISCLOSURE Polyimides of diamines and thianthrenetetracarboxylic acid 5,5,10,10-tetraoxides and poly(amide-acids) from which the polyimides are obtained.

This invention is directed to novel polyimides of diamines and thianthrenetetracarboxylic acid 5,5,10,10- tetraoxides and to certain poly(amide-acid) intermediates from which the polyimides are obtained.

It is an object of the present invention to provide novel filmand fiber-forming aromatic polyimides eX- hibiting outstanding physical and chemical properties including high thermal stability, resistance to hydrolysis, and retention of physical properties at elevated temperatures. Another object of the invention is to provide prepolymers as precursors for the novel polyimides which prepolymers are characterized by unexpectedly high solubility. Other objects of this invention will appear herein.

The novel aromatic polyimides of the invention are normally solid, high molecular weight polymers consisting essentially of the following recurring structural units:

reacting diamines and thianthrenetetracarboxylic dianhydride 5,5,10,10-tetraoxides having the structure 0 o I I NOF/J:

wherein the carbonyl groups are attached directly to separate carbon atoms on the aromatic rings and each pair of carbonyl groups is attached to adjacent carbon atoms on the aromatic ring to first produce normally solid, high molecular weight poly(amide-acids) consisting essentially of the following recurring structural units:

COOH B000 0 O S 2 \I wherein denotes isomerism and R is as defined above.

The resulting poly(amide-acids) may then be converted to the polyimides of this invention by suitable chemical or thermal treatment. The polyimides of this invention have an inherent viscosity of at least 0.1, preferably at least 0.3, the inherent viscosity being measured at 25 C. in a 0.5 percent solution of polymer in concentrated (96 percent) sulfuric acid. If the polyimide is not soluble in the acid to the extent of 0.5 percent, then its inherent viscosity is considered to be greater than 0.1.

The following equation will illustrate conversion of the poly(amide-acid) precursor to the polyimide of the invention:

O 02 ii S N 2I1H20 Sm C 0 (il n compounds are represented respectively by Formulas 1, 2, 3, and 4.

These compounds are suitably prepared by oxidation of the corresponding tetramethylthianthrene 5,5,10,10-tetraoxides with dilute nitric acid under auto'genous pressure and then conversion to the corresponding dianhydrides by the removal of two molecules of water using techniques well known in the art. i

The diamine reactants may be represented by the struc-' ture: 5

wherein R is a divalent organic radical which may be cyclic, heterocyclic, or acylic and includes a divalent aromatic, aliphatic, cycloaliphatic, combinations of aromatic and aliphatic; heterocyclic, bridged organic radicals wherein the bridge is, for instance, carbon oxygen, sulfur, nitrogen, phosphorus, silicon, and the like. The preferred R groups in the diamines are divalent organic radicals containing at least five carbon atoms, especially radicals of at least six carbon atoms characterized by benzoid unsaturati'cin such as arylene (e.g., phenylene, tolylene x ylylene, naphthylene, etc.), diarylene (e.g., diphenylene), and bridged aromatic radicals (e.g., diaryl ethers, silanes, sulfides, alkanes, and the like). Without limiting the invention to a specific numbefof diamines of this general structure, representative examples of suitable diamiries are phenylenedianrines; xylylenediamines; diaminodiphenyl etherrdiamino'diphenyl sulfone; diaminodiphenylrnethane; diaminodiphenylpropane; benzidine; Eliaminonaphthalenes; cyclobutanedianiines; cy elohexanediamines; cyclohexanebis(methylamines); hexamethylenediamine; hepta methylenediamine; bis(aminop'henyl) diethyl silane; bis (amino-phenynphosphine oxide; diaminodiphenyl sulfide; diaminopyridine; diamino cyclohexane; diamino alkanes; etc. Suitable examples are represented by the following formulae:

ngNrcnnmnr wherein X is a carbon, nitrogen; oxygen," silicon, phosphorus, or sulfur bridging atom, and n is an integer from 2 to l0. 7

The reaction. of dianhydrides and diamines, selected from the examples described above, is most advantageously carried out in a suitable inert solvent. Solvents used in the solution polymerization process for synthesizing the poly(amide-acid) of the present invention are relatively polar solvents whose functional groups do not react with either the dianhydrides or the diamines. Preferred solvents are the lower molecular members of the N,N-di alkylcarboxamide class such as N,N-dimethylforrnamide; RBI-dimethylacetamide; N,N-diethylformarnide; N,N-diethylacetarnide; and N-methyl-2-pyrrolidone. Dimethylsnlfoxide; 'N-acetyl-Z pyrrolidone; formamide; and methylformamide are also suitable solvents. Since water may react with dianhydrides and hydrolyze the poly {amide-acid) precursors at this stage, it is preferred to employ anhydrous solvents and conduct the reaction under anhydrous conditions. i

The conditions for the reaction of the dianhydrides and diamines of the invention can be varied considerably, but it is preferred to conduct the reaction at moderate temperatures, for example, about 20 to 100 C., preferably 0to 50 C. The simplest method of preparation is the slow addition of solid dianhydride to a stirred solution of diamine until maximum viscosity is attained. Since the reaction is exothermic, the reaction solution is cooled to maintain the desired reaction temperature. It is advisable to agitate the solution polymerization system after the additions of dianhydride are completed until maximum viscosity denoting maximum polymerization is obtained; a total reaction period of one to two hours is usually sufiicient. The amount of dianhydride required to give maximum viscosity is about one to five percent more than the theoretical amount ln the preparation of the poly(amideacid) intermediate the inherent viscosity of the polymer should be at least 0.1. The inherent yiscositylof the poly (amide-acid) is measured at'25 C. on a concentration of 0 .5 gram of polymer per 100 ml. of dimethylacetamide.

The amount of solvent ,used in the preparation of the p0ly(amide-acid)"should be sufficient to dissolve the diamine and the resulting polymer and should provide a polymer solution of suitable consistency for further operations, such as fiber or film preparation. It has "been found that the most successful results are obtained'when the fin al polymeric solution contains up to 30 percent by weightof polymer component.

Following the preparation of the poly(amide-aeid), this intermediate is'converted to the 'polyimide by the elimination of water. This cqnversion'can be accomplished by either chemical or thermal methods, or a combination of both; Examples of dehydrating agents suitable forjconverting poly(am ide-acidsj:- to polyIimides) are primary aliphatic acid anhydrides such as acetic anhydride, propionic' anhydride, butyric anhydride, etc. The conversion to polyim ide is also achieved by heating the poly(amide-acid) in a stream of an inert gas such as nitrogen.

This invention will be further illustrated by the following examples of preferred embodiments, although it will be understood that these examples are included merely for purposes of illustration and are not intended to liimt the scope of the invention. 5

EXAMPLE 1 e I A solution of 0.47 grarn (2.38 mole) of 4,4-methylenedianiline in 15 ml. of dimethylacetamide is stirred rapidly at 25 C. while one gram (2.38 mole) 0t 2,3,7,8-thianthrenetetracarboxylic dianhydrate 5,5,10,10-tetraoxide is slowlyadded. The inherent viscosity of the viscous dope is 1.11 (0.5 percent solution in dimethylacetamide).

The solution is cast onto glass plates, and thesolvent is evaporated in a stream of drynitrogenat C for 20 minutes. Poly -(amide-acid) films of excellent clarity and toughness are stripped from the plates.

6 The conversion to polyimide is carried out by heating converted to polyimides by thermal treatment. The data the poly(amide-acid) film in a stream of nitrogen, acis summarized in Table I.

TABLE I.-SUMMARY OF EXAMPLES 3-8 Dian- Solvent, ml. hydride, (dimethyl- Inherent acetamide) viscosity 1 Example Diamine, g.

1 Inherent viscosities of poly(amide-aeid) before conversion to polyimide, determined at a concentration of 0.5 gram polymer per 100 ml. in dimethylacetamide at C.

cording to the following program: heat from room tem- EXAMPLES 9-13 perature to 150 C. over an interval of an hour, then to 200 C. during minutes and hold at 200 C. for one In accordance with the general method described in hour, then heat to 300 C, over a period of two hour 20 Example 1, thianthrenetetracarboxylic dianhydride 5,5, and finally heat at 330 C. for 30 minutes. The polyimide 10,10-tetraoxides are added to various diamines, and films is a strong flexible film, yellow-brown in color. It does prepared from the poly(amide-acid) solutions are connot show evidence of appreciable degradation until it is verted to polymndes by thermal treatment. The resultheated to 440 C, mg compounds are summanzed in Table II.

TABLE II Thianthrenetetracarboxylic dianhydride tetraoxide Diamine Solvent 2, 3, 7, 8- 1,4 cyclohexanebis-(methylamine) Dimethyl formamide. 1,2, 7, 8- 1,6-hexanediamine Do. 1 1,2,7,8/2,3,7,8 4,4-methylenedianiline Dimethyl aeetamide. 1,2,7,8 2,2,4,4-tetrarnethyl-l,3-cyelobutanediamlne Dimethyl sulioxide. 13 1,2,7,8/2,3,7,8 Ethylene diamine N-methyl-pyrrolidone.

Mixture of isomers (approximately 60 obtained by oxidation of tetramethylthianthrenes derived from o-xyleno and sulfur chloride.

The polymer IS characterized by its insolubility in 501- It is well known in the reparation of polyimides of Vfints and basic reagents and y the appfiarance of the pyromellitic acid, that the poly(amide-acid) precursors imide bands at 5.6 and 13.8 mic o s i th infrared become insoluble when a relatively low percentage (less spectrum. than 30 percent of the amide-acid groupings) are con- EXAMPLE 2 verted to imide groups. It was quite unexpected to find in the present invention, that the poly(amide-acid) pre- ,f p y ether; 0-476 gram (2-38 mole) cursors of the thianthrenetetracarboxylic anhydride 5,5, 18 dlssolved In 15 of dlmetllylacetamlde, and 10,10-tetraoxides could be dehydrated to high imide congram mole) of 2,3,7,84h1anthrenetetaa{bX11 tent without becoming insoluble. Polymers still soluble dianhydride 5,5,10,10-tetraoxide is added portlonwise with 5 in polar Solvents were Prepared with as high as percent agitation at 25 C. The inherent viscos ty of the VlSCOllS f the amide acid groupings converted to imide linka,ges

p? is Thus,it is possible to determine the viscosity of a polymer Films f eXclleHt q y are from the PF and during the dehydration process up to a stage just short of dri d In an ve t 20 mlnutes- Converslon to complete imidization. In Table III, the inherent viscosities the polyimide is carried out as described in Example 1. 55 are listed f r oly(amide-acid) films prepared from 2,3, 7,8 thianthrenetetracarboxylic' dianhydride 5,5,10,10- EXAMPLES 3 8 tetraoxides and selected diamines and subjected to thermal As described in Example 1, 2,3,7,S-thianthrenetetracarimidization treatment at temperatures up to 250 C. Polyboxylic dianhydride is added to various diamines, and (amide-acids) of pyromellitic anhydride may tend to befilms prepared from the poly(amide-acid) solutions are Come insoluble by thermal treatment at 150 C. or less.

TABLE III.-INHERENT VISCOSITY l AT VARIOUS CURING TEMPERATURES Diamine 25 C. 80 0. 150 0. 200 0. 250 C.

1 Inherent viseosities were determined at a concentration of 0.5 gram polymer per ml. solution in dimethylaeetamide at 25 C.

2 Poly (amide-acid) solution (before preparation of film).

This unusual solubility of the polymers of the invention, even at relatively high conversion of the poly(amideacid) to the polyimide, presents a feature of considerable utility. A soluble polymer, suitable for preparation of films and spinning of fibers, can be prepared which requires substantially less chemical or thermal imidization treatment to produce the final insoluble polyimide. Furthermore, soluble prepolymers can be formulated in solutions of improved stability, lacking any tendency to gel formation from premature imidization. Solutions of poly(amide-acids) are generally not stable and show a decrease in inherent viscosity on storage; this effect is apparently due to moisture sensitivity of the amide-acid grouping. The polymers of the present invention permit the formulation of a solution of a more stable polymer, that is, a polymer with a high imide content and correspondingly lower percentage of moisture-sensitive amideacid linkages.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A normally solid, high molecular weight polyimide consisting essentially of the following recurring structural units:

0 I 02 O 9) ll wherein R is a divalent organic radical and the carbonyl groups are attached directly to separate carbon atoms on the aromatic rings and each pair of carbonyl groups is attached to adjacent carbons on the aromatic rings, said polyimide having an inherent viscosity of at least 0.1 measured at C. in a 0.5% solution of polyimide in concentrated sulfuric acid.

2. A polyimide as defined by claim 1 wherein R is a divalent hydrocarbon radical.

3. A polyimide as defined by claim 2 wherein the divalent hydrocarbon radical is a divalent aromatic radical.

4. A polyimide as defined by claim 2 wherein the divalent hydrocarbon radical is a divalent aliphatic radical.

5. A normally solid poly(amide-acid) consisting essentially of the following recurring structural units:

COOII B000 02 7 s I Lj f}? 02 o N R L at I wherein denotes isomerization, R is a divalent organic radical, and the carbonyl groups are attached directly to separate carbon atoms on the aromatic rings and each pair of carbonyl groups is attached to adjacent carbons on the aromatic rings, said poly(amide-acid) having an inherent viscosity of at least 0.1 measured at 25 degrees C. on a concentration of 0.5 gram of polymer per ml. of dimethylacetamide.

6. A poly(amide-acid) as defined by claim 5 wherein R is a divalent hydrocarbon radical.

7. A poly(amide-acid) as defined by claim 6 wherein the divalent hydrocarbon radical is a divalent aromatic radical.

8. A poly(amide-acid) as defined by claim 6 wherein R is a divalent aliphatic radical.

9. A film of a polyimide as defined by claim 1.

10. A fiber of a polyimide as defined by claim 1.

References Cited UNITED STATES PATENTS 3,179,614 4/1965 Edwards 260-30.2 3,179,634 4/1965 Edwards 26078 3,356,648 12/ 1967 Rogers 26047 3,410,868 11/1968 Harris 260327 3,414,543 12/1968 Paufler 26047 3,420,795 1/1969 Angelo 26047 WILLIAM H. SHORT, Primary Examiner H. SCHAIN, Assistant Examiner U.S. Cl. X.R.

P0'1050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 5,502 ,625 Dated March 24 1970 Inventor(s) Melvin Harris It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 69, the word "dianhydrete" should be q ---dianhydride---; Column 6 Table III, the second formula should read Column 6 Table III, the second number under the sub-heading "200C." should read ---0.92---; Column 7, lines 29-37, the formula should read O O l! l 1g 1g N e I /N-R-- ii if 02 O O J o'IGNED ANL: QEALED oars-m Arrest:

Edward M.Fletcher,]'n

mm E W: JR- Aueshng Offiwl Commissioner of Patents 

